If you’ve ever selected a valve before, you know there’s a lot of things to consider. You need to know what type of valve is best for your application, the proper materials of construction for best performance, how the valve should be actuated, among other things. But one of the most important things to know for sizing/selecting a valve is its Flow Coefficient or Cv.
What is Flow Coefficient (Cv)?
The Cv tells you how to properly size your valve so it has minimal effect on the hydraulic efficiency you’ve engineered into your system. It is a number published by the valve manufacturer that describes the number of U.S. gallons that can pass through a valve (in a fully open position) at a pressure drop of 1 PSI.
Why You Should Care
Knowing and understanding your Cv can help you in a number of ways:
- Quickly compare different brands of valves and their flow capacities
- Help to select a valve that is the right size (and not oversized) for the application
- Quickly understand how the valve you select will have an effect on the pressure in your system
Where does Cv come from, and where can I find it?
Cv is determined by the manufacturer of the valve and can be found on the valve manufacturer's website and/or related valve data and specification sheets. Valves are tested by running water through it before publishing the Cv value. It can be assumed that the tests are done with water (unless otherwise noted), using a specific gravity of 1.0, 1.2 centistoke viscosity, and a standard temperature of 60 degrees Fahrenheit. If you're not passing water through the valve, adjustments will need to be made to the flow coefficient to determine the correct pressure drop.
Click here for more information about valve sizing and Cv formulas.
Need help determining the correct Cv value for your valve and fluid? There are multiple calculators available on the internet. If you need further assistance, contact a valve distributor to help you get it right.